The invention relates to a developer sleeve or carrying element that has a wear resistant coating that provides optimum print quality for a toner cartridge that prints 30,000 pages.
A developer sleeve is used in an electrophotographic toner cartridge to carry toner to the developing gap. The developer sleeve is comprised of an aluminum core, which may be surface treated, and a coating having a thickness of approximately 5-10 microns. The significance of the coating is to provide 1) the proper surface roughness to carry the toner, 2) the proper electrical conductivity and triboelectric characteristics to charge the toner and 3) to provide a surface that will not allow the toner particles to permanently adhere and thus be free to move within the developing gap.
Various patents have been issued relating to the developer sleeve and specifically the coating. Below is a list of the existing developer sleeve patents.
In U.S. Pat. No. 4,989,044, dated Jan. 21, 1991, there is described a coating that contains a phenolic resin, graphite, and carbon black. The coating was applied to the core to reduce fade to black (low optical density of first developer revolution) and to prevent optical density from decreasing over life. The coating stabilizes the toner charge throughout life and across all environments. In addition, the coating prevents the toner from being deposited on the developer sleeve.
In U.S. Pat. No. 5,164,780, dated Nov. 17, 1992, the surface characteristics (specifically Cv at tp=5%) of the sleeve must be controlled to prevent ghosting. The Cv at tp=5% should be between 0.5 and 5 micrometers. In addition, the surface characteristics of the sleeves may be controlled by polishing the coating after dipped or sprayed on the core.
In U.S. Pat. No. 5,185,496, dated Feb. 9, 1993, the specific surface characteristics necessary to prevent fade to black and ghosting from occurring are described. The average roughness should be between 0.4 and 3 micrometers Ra, the coating thickness should be between 1 and 30 microns and the volume resistivity should be between 0.001 and 100 ohm-cm.
In U.S. Pat. No. 5,274,426, dated Dec. 28, 1993, there is described polishing of the coating layer of the sleeve on the ends different from the middle. This is to prevent fade to black on the printed pages. An alternative to polishing is to use a different coating at the ends of the sleeve versus the middle.
In U.S. Pat. No. 5,286,917, dated Feb. 15, 1994, the surface characteristics of the core should be controlled to between 1.0 and 3.0 micrometers Ra by sandblasting the core. The sandblasted core improves adhesion of the coating to the core, prevents wear, and suppresses a change in the coating surface characteristics throughout the life of printing. Also, this patent shows refining the coating surface characteristics to be an average roughness, Ra, between 0.8 and 2.5 micrometers, the average pit to pit spacing, Sm, to be 30 to 70 micrometers, and the coating layer to be deposited on the core as 4 to 12 g/m2.
Finally, in U.S. Pat. No. 5,547,724, dated Aug. 20, 1996 (JP application priority date of Oct. 2, 1989), there is described adding a spherical polymeric material (PMMA) to the coating to provide a coating whose surface characteristics do not change over a duration of printing a large number of pages. In addition the patent claims that this coating will allow a stable charge to the toner in all environments. The polymeric material is added to a coating of phenolic resin, graphite and/or carbon black.
Based on the listed patents above, and others, coating formulations were used for existing cartridges.
40-60% of solids is natural graphite (specifically 52-57%) PA1 40-60% of solids is phenolic resin (specifically 42-47%)
This formula is shear mixed and milled at a 20-24% solids loading into denatured ethanol. The wet coating is then sprayed onto sandblasted aluminum cores (core Ra between 1.5 and 2.5 micrometers) with a coatweight between 0.15 and 0.30 g and more specifically 0.1 8-0.25 g (for a coating area of approximately 170 cm.sup.2). The coating is cured in a convection type oven at between 165.degree. C. and 175.degree. C. for 30 minutes. The finished coating has an Ra between 1.9 and 3.0 micrometers and a Cv at tp=5% of &lt;6 microns. This sleeve, when used with the existing cartridge system, has a coating durability of at least 15,000 pages and an average optical density through the life of a cartridge of between 1.35 and 1.50.
With the market demand for higher speed printing and longer life cartridges, it is an objective of the present invention to produce a developer sleeve that will not only have excellent print quality for the entire life of the cartridge, but also will be able to have a coating that is more durable and resists wearing off of the core. No patents exist that describe a solution for coating wear resistance of this type.
The toner cartridge utilizes a developer sleeve to carry toner on its surface from the toner supply container to the development zone. This sleeve utilizes a coating with a specified roughness and electrical properties to produce the proper mass and charge of the toner. The specified roughness and electrical properties need to be maintained over the life of the toner cartridge in order to maintain the desired print performance. Any change in these characteristics result in print defects such as loss of optical density, poor uniformity of gray scale printing, high levels of background printing, etc.
It is a further object of the present invention to produce a toner cartridge that has a cycle life of 30,000 pages.